<!DOCTYPE html>
<html>
  <head>
    <style>
      #good {
        background-color: green;
      }
      .abs {
        position: fixed;
        margin: 0;
        padding: 0;
        top: 25px;
        left: 25px;
        width: 50px;
        height: 50px;
        background-color: green;
      }
    </style>
  </head>
  <body>
    The green square should completely cover the red square.
    <div class="abs" id="good"></div>
  </body>
</html>
